func selectDriver()

in cmd/minikube/cmd/start.go [578:682]
90 lines of code
27 McCabe index (conditional complexity)

func selectDriver(existing *config.ClusterConfig) (registry.DriverState, []registry.DriverState, bool) {
	// Technically unrelated, but important to perform before detection
	driver.SetLibvirtURI(viper.GetString(kvmQemuURI))
	register.Reg.SetStep(register.SelectingDriver)
	// By default, the driver is whatever we used last time
	if existing != nil {
		old := hostDriver(existing)
		ds := driver.Status(old)
		out.Step(style.Sparkle, `Using the {{.driver}} driver based on existing profile`, out.V{"driver": ds.String()})
		return ds, nil, true
	}

	// Default to looking at the new driver parameter
	if d := viper.GetString("driver"); d != "" {
		if vmd := viper.GetString("vm-driver"); vmd != "" {
			// Output a warning
			warning := `Both driver={{.driver}} and vm-driver={{.vmd}} have been set.

    Since vm-driver is deprecated, minikube will default to driver={{.driver}}.

    If vm-driver is set in the global config, please run "minikube config unset vm-driver" to resolve this warning.
			`
			out.WarningT(warning, out.V{"driver": d, "vmd": vmd})
		}
		ds := driver.Status(d)
		if ds.Name == "" {
			exit.Message(reason.DrvUnsupportedOS, "The driver '{{.driver}}' is not supported on {{.os}}/{{.arch}}", out.V{"driver": d, "os": runtime.GOOS, "arch": runtime.GOARCH})
		}
		out.Step(style.Sparkle, `Using the {{.driver}} driver based on user configuration`, out.V{"driver": ds.String()})
		return ds, nil, true
	}

	// Fallback to old driver parameter
	if d := viper.GetString("vm-driver"); d != "" {
		ds := driver.Status(viper.GetString("vm-driver"))
		if ds.Name == "" {
			exit.Message(reason.DrvUnsupportedOS, "The driver '{{.driver}}' is not supported on {{.os}}/{{.arch}}", out.V{"driver": d, "os": runtime.GOOS, "arch": runtime.GOARCH})
		}
		out.Step(style.Sparkle, `Using the {{.driver}} driver based on user configuration`, out.V{"driver": ds.String()})
		return ds, nil, true
	}

	choices := driver.Choices(viper.GetBool("vm"))
	pick, alts, rejects := driver.Suggest(choices)
	if pick.Name == "" {
		out.Step(style.ThumbsDown, "Unable to pick a default driver. Here is what was considered, in preference order:")
		sort.Slice(rejects, func(i, j int) bool {
			if rejects[i].Priority == rejects[j].Priority {
				return rejects[i].Preference > rejects[j].Preference
			}
			return rejects[i].Priority > rejects[j].Priority
		})

		// Display the issue for installed drivers
		for _, r := range rejects {
			if r.Default && r.State.Installed {
				out.Infof("{{ .name }}: {{ .rejection }}", out.V{"name": r.Name, "rejection": r.Rejection})
				if r.Suggestion != "" {
					out.Infof("{{ .name }}: Suggestion: {{ .suggestion}}", out.V{"name": r.Name, "suggestion": r.Suggestion})
				}
			}
		}

		// Display the other drivers users can install
		out.Step(style.Tip, "Alternatively you could install one of these drivers:")
		for _, r := range rejects {
			if !r.Default || r.State.Installed {
				continue
			}
			out.Infof("{{ .name }}: {{ .rejection }}", out.V{"name": r.Name, "rejection": r.Rejection})
			if r.Suggestion != "" {
				out.Infof("{{ .name }}: Suggestion: {{ .suggestion}}", out.V{"name": r.Name, "suggestion": r.Suggestion})
			}
		}
		foundStoppedDocker := false
		foundUnhealthy := false
		for _, reject := range rejects {
			if reject.Name == driver.Docker && reject.State.Installed && !reject.State.Running {
				foundStoppedDocker = true
				break
			} else if reject.State.Installed && !reject.State.Healthy {
				foundUnhealthy = true
				break
			}
		}
		if foundStoppedDocker {
			exit.Message(reason.DrvDockerNotRunning, "Found docker, but the docker service isn't running. Try restarting the docker service.")
		} else if foundUnhealthy {
			exit.Message(reason.DrvNotHealthy, "Found driver(s) but none were healthy. See above for suggestions how to fix installed drivers.")
		} else {
			exit.Message(reason.DrvNotDetected, "No possible driver was detected. Try specifying --driver, or see https://minikube.sigs.k8s.io/docs/start/")
		}
	}

	if len(alts) > 1 {
		altNames := []string{}
		for _, a := range alts {
			altNames = append(altNames, a.String())
		}
		out.Step(style.Sparkle, `Automatically selected the {{.driver}} driver. Other choices: {{.alternates}}`, out.V{"driver": pick.Name, "alternates": strings.Join(altNames, ", ")})
	} else {
		out.Step(style.Sparkle, `Automatically selected the {{.driver}} driver`, out.V{"driver": pick.String()})
	}
	return pick, alts, false
}